Several microtubule-associated proteins (MAPs) , including MT-dependent motor enzymes, have been localized to components of the mitotic apparatus by light microscopic immunocytochemistry. This observation implicates such molecules in chromosome movement, but does not elucidate the specific role that they play or the mechanism by which they work. We are cloning genes for mitotic MAPS and motors, then making antibodies to the corresponding gene products expressed in bacteria in order both to have tools to disrupt motor function and to localize motors at high resolution within spindle. Methods are being developed to permit immunolocalization of motor enzymes at good EM resolution on both and sections of mitotic spindles. Whole mounts of chromosomes interacting with microtubules in vitro are also under study. Through these approaches we hope to determine the localization and binding sites of different motor molecules. Such information will help us learn the role these enzymes play in chromosome movement. We have determined the location of one kinesin-like motor enzyme with EM-immunocytochemistry, demonstrating that it is not only in the region of the spindle identified in the light microscope, but also elsewhere, associated with spindle MTs at lower concentrations.